1. Field of the Invention
This invention relates generally to the field of oil and gas field drilling and casing, and, more particularly, to a tool for pushing and rotating a casing that is being floated into a wellbore. The casing pushdown and rotating tool is particularly effective in floating a casing into a horizontal or extended reach wellbore.
2. Description of the Related Art
The field of drilling sometimes requires pushing casing into substantially horizontal wells. This becomes necessary when, for example, a formation sought to be tapped into using a well is in a location that cannot be reached from a substantially vertical well because of the potential adverse environmental impact associated with drilling from a position directly above the formation, or because increased production is possible from a horizontal or extended reach wellbore. When it is necessary to insert casing into a substantially horizontal well, for example, inserting a casing into a well that extends vertically only a few thousand feet from the surface but extends several thousand feet horizontally, the casing is sometimes pushed. When the wellbore is of substantial length, the frictional forces associated with pushing the casing as it lays on the bottom of the wellbore become significant, to the point where it becomes necessary to try something else to continue the progression of the casing string. One such method used to extend the reach of the casing into the well is to hold the casing off the bottom of the well. This is possible with a procedure called floating. When a casing is floated into a well it is held off the bottom of the casing by floating on a fluid, usually drilling mud, which is already in the wellbore. The casing is run into the well empty, and as it is inserted into the mud-filled well, a buoyancy force keeps the casing floating off the bottom of the well. It is then easier to push the long casing string to the bottom of the well. However, the buoyancy of the casing can also present a problem. In some wells the casing has a tendency to "kick back" and come out of the wellbore because of the buoyancy force created as the casing is inserted into the wellbore. For this reason there is a need to hold and push the casing as it is being inserted into the wellbore.
In addition, sometimes during the insertion of the casing, the casing may become stuck and can be very difficult or impossible to dislodge and continue to advance through the wellbore by simply pushing. This happens because the wellbore is not a perfectly straight hole for the length of the well. The horizontal section of a well naturally has small peaks, valleys, twists, and turns that the casing can often get hung up and stuck on as it is floated into the hole. Current methods of dislodging a stuck casing include rotation of the casing using a water bushing. The rotation of the casing while concurrently advancing the casing causes a corkscrew effect, which often frees the stuck casing. The installation and use of a water bushing, however, requires significant amounts of time and money. Until the present invention, there was no way to allow holding, pushing, and rotation of the casing without a time consuming and expensive interruption of the lowering of the casing into the wellbore to install a water bushing.
A water bushing is connected to the top drive via a drill pipe or pup joint and then in turn connected to the casing string hanging in the wellbore. The top drive rotation mechanism is used to rotate the complete casing string. This method has both cost and safety implications, i.e. the casing operation has to be halted while the water bushing is fitted to the top drive and casing string. During that period, which can take up to one hour, it is possible that because of the lack of movement the casing will become completely stuck and thus a well intervention method might have to be deployed to release the casing. In such a circumstance several days can be lost. There is also a safety concern associated with installing a water bushing. If the casing is stuck at a high point above the rig floor, then a person in a riding belt has to negotiate the water bushing makeup high above the floor, creating a safety risk.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.